The invention relates to a dental tool for root canal preparation.
Recent endodontic studies have discussed various methods of root canal preparation. The authors of some of these studies have raised questions about the effectiveness of hand instruments and have preferred the ease of use and efficiency of time of rotary instruments. The elimination of morphologic aberrations from the canal is important for debris removal and also to effect smoothness of the intracanal walls for ease of filling. However, no matter what rotary instrument is used, some hand instrumentation must be done, but the bulk of the canal preparation can be accomplished by a properly designed rotary instrument. In this manner the labor involved, in using the final hand instrument at the curved tip (apex) of the root canal, is reduced. Clinical studies have shown the importance of flaring the canal for debridement and instrumentation, and to allow the placement of more irrigating solution into the canal for disinfection and cleansing. Today many dentists use a combination of rotary instruments to widen or flare the orifice, cervical, and middle portions of the canal, allowing the apical portion to be easily accessed for final hand instrumentation.
The prior art instrument commonly used for this purpose is the Gates-Glidden drill. This drill has a short flame-shaped, pear-shaped, head with side cutting blades spiraling slightly with a wide rake angle. A Gates-Glidden drill usually has a short non-cutting guide at the tip to minimize its potential for perforating the root surface of the canal, but can also be obtained without the non-cutting guide. The flame-shaped head is connected to the shank by a long thin neck. The tip has been known to break during use, thus preventing further root canal treatment. Unintentional perforations are also common with drills of the Gates-Glidden type, the #1 drill being equal to a #40 hand file instrument which is larger than typical root canals. The #40 hand instrument is used only after much preparation, and usually in straight canals. Instruments normally used in root canal work include a hand instrument of #15 which has a 0.15 mm tip. Others so used include #20, #25, #30 etc., being 0.05 mm larger, incrementally. Therefore, it is apparent the #1 Gates drill (0.40 mm) is too large for root canal work. The #2 Gates drill is the size of a # 60 (0.60 mm tip) hand instrument, while the #3, 4, 5 and 6 Gates drills are 0.80, 1.0, 1.2, and 1.4 mm, respectively. Most rotary instruments have a tendency to transport at least part of the root canal, particularly in curved canals. Often a portion of the root canal has not been touched by the drill, leaving residual tissue, which may result in further contamination. The Gates drill will straighten canals and leave only an apical curve. Due to its pear shape, the Gates drill will notch and furrow the internal wall of the canal, leaving it grooved and forming a repository for debris. As a result, more hand instrumentation is necessary. Due to the pear shape, debris is forced ahead of the drill, instead of being withdrawn by the drill, allowing dentin particles to remain in the canal, requiring further hand instrumentation and irrigation.